The invention relates to an original conveying apparatus for an electrophotographic copying machine, and more particularly, to such apparatus for conveying an original having substantial thickness which is used in the electrophotographic copying machine of the type capable of carrying, not only a sheet-shaped, thin original, but also an original having substantial thickness, such as a book, to an exposure station for copying purpose, with a book carrier being utilized to convey the thick original.
As is well recognized, a conventional electrophotographic copying machine of the type in which an original is fed through an exposure station for copying purpose is constructed as illustrated in FIG. 1, for example. The machine is provided with an original feed path which is normally conditioned to enable copying from a single sheet-shaped original, as shown. In the condition shown, a sheet-shaped original 1 is placed on an inclined original receptable 2, and is inserted into the inlet of an original conveyor unit which includes pairs of conveyor rollers 4A, 4B and 5A, 5B and a pair of guide plates 6, 7. After passing through the inlet, the original 1 is fed into the nip between the pairs of vertically spaced conveyor rollers 4A,4B to be fed toward and through an exposure station 8 while passing between the guide plates 6, 7 and between the guide plate 6 and the exposure station 8. After passing through the exposure station 8, the original is fed into the nip between the other pair of vertically spaced conveyor rollers 5A, 5B to be delivered onto an original tray 9.
As the original 1 is fed by the original conveyor unit, a pair of microswitches 3A, 3B, located adjacent to the rollers 4A, 4B, detect the position of the original 1, and the timing of operation of the various parts of the electrophotographic copying machine is controlled based upon this detection. As the original 1 passes through the exposure station 8, an illumination lamp 10 illuminates the surface of the original, whereupon an exposure optical system 11 projects an image of the original onto a photosensitive drum 12. The drum 12 rotates in a direction indicated by an arrow B. Any electric charge is initially removed from the drum surface by means of a neutralizer lamp 13, and then the drum surface is uniformly charged by means of a corona charger 14. Then the drum surface is irradiated with the light image of the original to have an electrostatic latent image of the original 1 formed thereon. The latent image is developed by a developing unit 15 of dry type to form a toner image, which is moved to a transfer station 16 as the drum 12 rotates.
On the other hand, a record sheet 18 is fed one by one from its stack contained in a cassette 17 by means of a rocking and rotating feed roller 19, and is fed to the transfer station 16 by a pair of vertically spaced feed rollers 20 in timed relationship with the rotation of the drum so that the record sheet is superimposed on the toner image on the drum surface. Thereafter, the record sheet is conveyed between the drum 12 and a transfer roller 21 to which a bias voltage is applied. Such process transfers the toner image onto the record sheet. Since the record sheet is conveyed in firm contact against the drum surface during the process, the sheet must be separated from the drum surface by utilizing a separation claw 22 which cooperates with an airstream, as will be described later. After the transfer step, the record sheet is conveyed along a guide plate 23 to be fed, by a pair of vertically spaced feed rollers 24, into a fixing unit 25 which includes a heater where the toner image is fused and fixed to the record sheet. Subsequently, the sheet is delivered onto a copy tray 27 by means of a pair of vertically spaced delivery rollers 26.
Any residue of toner which remains on the drum surface after the transfer step is removed by a rotating cleaning brush 28, which removed toner is withdrawn by an airstream created by a fan 29 to be collected in a filter 30. Both the cleaning brush 28 and the fan 29 are covered by a casing 31 in order to produce an effective withdrawal effect upon the toner residue and to prevent a dispersion of the toner into the apparatus. An airstream displaced by the fan 29 is introduced into a duct 32 having its outlet port 32a located adjacent to the transfer station 16, so that the airstream is effective to separate the record sheet from the drum 12 by cooperation with the separation claw 22.
The disclosed copying machine is designed so that an electrostatic latent image once formed on the drum surface may repeatedly be used to provide a plurality of copies in succession through a repeated process of developing with toner and image transfer. In this instance, the cleaning brush 28, which is mounted on a holding member 34 rotatably mounted on a support shaft 33, is moved away from the drum 12 and the neutralizing lamp 13 and the charger 14 are maintained inoperative.
Such copying machine is normally used to provide a copy or copies from a single sheet-shaped original, but can be operated to provide a copy from an original having an increased thickness such as a book in a manner to be mentioned below. Specifically, a follower roller unit 35 which is adapted to define an extension of a conveying path and including the upper conveyor rollers 4B, 5B, which are constructed as follower rollers, and also including the guide plate 6 is pivotally mounted on a pin 36 so as to be turned through 180.degree. in a direction indicated by an arrow C. When so turned, these rollers and the guide plate 6 define an extension of the conveying path which is contiguous with the exposure station 8 and which is located above the original tray 9 (see FIG. 2).
A book carrier for placing a thick original can now be used. A book carrier having a thick original placed thereon is initially placed on the original receptacle 2, and is conveyed toward the exposure station 8 by means of conveyor rollers 4A, 5A, which act as drive rollers during a copying operation and which cooperate with their associated drive members. As the book carrier passes through the exposure station, the original is irradiated through a transparent plate 51 on which it is placed, whereby a copying operation takes place.
Referring to FIGS. 2 and 3, a book carrier and an associated conveyor unit will be described more specifically. A book carrier 50 comprises a rectangular transparent plate 51 of a relatively flexible material such as thin plastics on which a book or the like may be disposed with the surface of original to be copied placed in abutment against the transparent plate 51. The carrier also comprises a rectangular, tray-shaped support 52 having a bottom surface in the form of a picture frame on which the transparent plate 51 is centrally disposed in a detachable manner. The support 52 is lengthwise driven from a location on the original receptacle 2 toward the exposure station 8, by a drive member to be described later, during a copying operation. A substantially V-shaped book retainer 53 formed by resilient wire is disposed lengthwise in the central portion of the support 52, and has its opposite ends releasably mounted in a pair of detent holes formed in tabs 54 which are integral with each of the sideplates 52b, 52b of the support 52. The apex portion of the book retainer 53 is rotatably received in a holder 55 which is integrally formed on the support 52. In this manner, a book can be held between the wire and the transparent plate 51 in a condition such that the book lies against an inclined front bottomplate 52a of the support 52, which represents the front end of book carrier 50. When the book carrier 50 is used, the frame 35 is turned 180.degree. in the direction of the arrow C (see FIG. 1) about the pin 36 to locate the conveyor rollers 4A, 5A, 4B, 5B, the guide plates 6, 7 and the exposure station 8 all exposed as mentioned previously. The guide plate 7 and the original receptacle 2 are formed with guide grooves 7a, 2a of a lower elevation than their associated central surfaces in order to facilitate guiding the book carrier 50. Disposed in one of the guide grooves 7a are a pinion 40 which represents a drive member for the book carrier and which is mounted on the same drive shaft 4C (see FIG. 3) as the conveyor rollers 4A, and another pinion 41, also representing another drive member, which is mounted on the same drive shaft as the conveyor rollers 5A. A pair of retainer plates 44 are secured to the upper surface of the sideplates 43, located outside of the guide grooves 7a, so as to extend horizontally over their respective guide grooves 7a so that they constrain the book carrier 50 from shifting upward as the latter reaches the location of these retainer plates 44.
To permit free movement of the book carrier 50 while avoiding undesirable contact of its central lower surface with the original receptacle 2 when it is placed on the receptacle 2, both sideplates 52b of the support 52 have respective lower extensions which bear against the bottom surface of the guide grooves 2a formed on the opposite sides of the original receptacle 2. A pair of horizontal ledges 52c (see FIG. 3) are integrally formed with the lower end of each of the sideplates 52b, and that one of the ledges which is aligned with the pinions 40, 41 when the book carrier 50 is placed on the original receptacle 2 with the front bottomplate 52a facing the exposure station 8, is formed with a rack 56 (see FIG. 3) along its lower surface. The rack 56 represents a driven member which meshes with the pinions 40, 41 to feed the book carrier, and is arranged to avoid its abutment against the bottom surface of the guide grooves 2a formed in the original receptacle 2. A pair of ledges 52d are formed on the inside of each of the sideplates 52b of the book carrier 50, and grooves 57 (see FIG. 3) are formed therein so as to extend horizontally. The opposite lateral edges of the transparent plate 51 are detachably fitted into the grooves 57.
In the conveying apparatus constructed as mentioned above, the follower rollers 4B, 5B which are mounted in the follower roller unit 35 together with the guide plate 6 must exhibit a frictional force of a suitable magnitude when the unit 35 is not deployed and the follower rollers are located opposite to the drive rollers 4A, 5A to convey a sheet-shaped original held therebetween. It is also necessary that a sheet-shaped original having an increased thickness can also be inserted into the nip between the rollers 4A, 5A and 4B, 5B. Accordingly, the unit is resiliently urged by a leaf spring 66, as shown in FIG. 1, so as to project above the original guide surface 6a of the guide plate 6, as will be further discussed later.
However, when the follower roller unit 35 is deployed to the position shown in FIG. 2, and the carrier 50 is conveyed over the original guide surface 6a of the guide plate 6, the weight of the carrier inclusive of a book placed thereon or pressure applied thereto in order to obtain a frictional force of a suitable magnitude causes the follower rollers 4B, 5B to be depressed against the resilience of the leaf spring 66 to a point where the transparent plate 51 of the carrier 50 directly bears against the original guide surface 6a of the guide plate 6, resulting in a sliding contact therewith. Consequently, as the carrier 50 reciprocates repeatedly, the lower surface of the transparent plate 51 is rubbed against the original guide surface 6a to be damaged. Damages caused to the transparent plate 51 are also copied, resulting in a whitening of a black image area or letters becoming thin to degrade the image quality. In this manner, the copying performance is greatly degraded.